Electronic states of neutral and ionized tetrahydrofuran studied by VUV spectroscopy and ab initio calculations

Abstract

The electronic spectroscopy of isolated tetrahydrofuran (THF) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 5.8-10.6 eV with absolute cross section measurements derived. In addition, an electron energy loss spectrum was recorded at 100 eV and 10° over the 5-11.4 eV range. The He(I) photoelectron spectrum was also collected to quantify ionisation energies in the 9-16.1 eV spectral region. These experiments are supported by the first high-level ab initio calculations performed on the excited states of the neutral molecule and on the ground state of the positive ion. The excellent agreement between the theoretical results and the measurements allows us to solve several discrepancies concerning the electronic state spectroscopy of THF. The present work reconsiders the question of the lowest energy conformers of the molecule and its population distribution at room temperature.

Total, elastic, and inelastic cross sections for positron and electron collisions with tetrahydrofuran

“…Nevertheless, at room temperature the population of conformers in our THF sample is expected to be essentially dominated by nearly the same proportion of the two most energetically stable conformers, i.e., those in the C 2 (55.5%) and C s (44.5%) geometry. 21 It is interesting to note that these two lowest energy conformers share the same values for the dipole moment and the dipole polarizability (see above). 18 Therefore, the presence of more than one conformer in our THF sample might not significantly complicate the interpretation of our experimental results.…”

A dynamical (e,2e) investigation of the structurally related cyclic ethers tetrahydrofuran, tetrahydropyran, and 1,4-dioxane

“…[32][33][34][35] On the one hand, THF has a relatively flat 5-member ring that possesses puckering out of the planar configuration, with the flatness of this ring structure producing a number of conformations that lie close in energy. Further, low potential energy barriers for pseudo-rotation between its conformations enable essentially free rotation between minima.…”

“…Further, low potential energy barriers for pseudo-rotation between its conformations enable essentially free rotation between minima. 32,33 As such, THF exists in conformers with either C 2 or C s symmetry found along the pseudorotation coordinate. 32,33 On the other hand, it has been well established that both THP and 1,4-dioxane exist in their lowest energy chair conformations.…”

“…32,33 As such, THF exists in conformers with either C 2 or C s symmetry found along the pseudorotation coordinate. 32,33 On the other hand, it has been well established that both THP and 1,4-dioxane exist in their lowest energy chair conformations. 34,35 These, respectively, have C s and C 2h symmetries.…”

“…In the interest of making fruitful comparisons regarding the behavior of these three cyclic ethers, we consider THF through an average over the C 2 to C s conformations; with experimental results having revealed that both conformations exist in near equal proportions at roomlike temperatures. 32,33 As our experiment is performed under room-like temperature conditions, this is a reasonable approximation given the complexity of the calculations. The full details of this averaging approach have been described elsewhere.…”